docs: def _exclude_ss_bonded_cysteines(self):
          """
          Pre-compute ss bonds to discard cystines for H-adding.
          """
          
          ss_bonds =  self.nh_structure.search_ss_bonds()
          for cys_pair in ss_bonds:
              cys1,  cys2 = cys_pair
              
              cys1.resname = 'CYX'
              cys2.resname = 'CYX'